DESCRIPTION (adapted from abstract): The striatum is the major entrance of information to the basal ganglia, a group of interconnected brain structures that play major roles in the control of motor behaviors. The activity of striatal neurons is under the influence of two major excitatory synaptic inputs that arise from the cerebral cortex and the caudal intralaminar thalamic nuclei, namely the centromedian (CM) and parafascicular (PF) nuclei. Despite the fact that the existence of a thalamostriatal pathway has long been established, and that the CM reaches its maximum extent in primates, the role of thalamic influences upon striatal neurons is usually not considered in the functional circuitry of the basal ganglia. Although the functions of the intralaminar nuclei are complex and multifaceted, it is well known that CM plays a role in maintaining a state of high vigilance and attention, two features that might be critical for alerting and preparing striatal neurons for incoming input. Over the past five years, the investigator carried out a series of studies that demonstrate the large extent and high degree of functional and synaptic specificity of the CM afferents to striatal neurons in monkeys. He now proposes to elucidate the sources of synaptic inputs to thalamostriatal neurons to obtain a better understanding of the nature of information that flows through the thalamostriatal pathway. Four hypotheses will be tested in the project: 1) they will test the possibility that the CF/PF nuclear complex is part of functionally distinct circuits with neurons in the basal ganglia, 2) they will verify whether individual thalamostriatal neurons might be the site of convergence of cognitive- and limbic- related information from the basal ganglia, 3) they will test the possibility that thalamostriatal neurons are targets of ascending cerebellar influences and, therefore, represent a major link through which a copy of the cerebellar information is conveyed to striatal neurons and 4) they will better characterize the synaptic relationships and neurotransmitter content of the ascending reticular activating system from the tegmental pedunculopontine nucleus that impinge upon thalamostriatal and thalamocortical neurons in CM. The results of the project, combined with previous data, are prerequisite to future functional studies of the thalamostriatal projection in normal and pathological conditions.